This invention relates to laminate composite materials that can be easily torn by hand in both the machine direction and the cross direction, and to a method of making such laminate composites.
Adhesive tapes are commonly constructed of one or more layers of fabric and are sold to consumers in rolls containing several feet of material wrapped around a core. The person who uses the tape must then cut or tear a small length of material from the roll, often no more than an inch or two, as needed from time to time. As virtually every one knows, tearing off such a small length of tape by hand, without the aid of a scissors or other sharp edged instrument, is a vexing task, which often results in failure and a tangled mess. This problem is well known in the tape making art, and many have tried to solve it with various methods designed to impart some measure of xe2x80x9cfinger tearabilityxe2x80x9d to the fabric of the tape.
It is especially difficult to tear tapes made with nonwoven backings. One approach taken in the art to address the problem has been to emboss patterns on the tape fabric to provide xe2x80x9ctear linesxe2x80x9d on its surface, along which it is hoped the tearing force will be concentrated so that a piece of tape may be torn in an even line from a roll. PCT patent document No. WO93/15245, for example, discloses a nonwoven sheet material, suitable for use as a tape backing, that has an embossed pattern on its surface and is readily finger-tearable in both the machine direction and the cross direction. The nonwoven web preferably comprises randomly interlaced, tensilized nonfracturable staple fibers and binder fibers. The web is embossed by feeding it between two opposing rolls, one of which is a calender roll having an engraved pattern on its surface.
Another approach taken has been to treat the nonwoven tape fabric with chemicals to form tear lines. U.S. Pat. No. 4,772,499 discloses a tape that is made finger-tearable by the patterned impregnation of a bonding agent throughout the thickness of the nonwoven tape backing. The bonding agent may be a latex and is applied in a series of parallel lines across the width, or cross direction, of the tape.
Other workers have attempted to increase the finger-tearability of nonwoven tapes by combining nonwoven layers with layers of other polymeric materials. U.S. Pat. No. 5,246,773 discloses a tape that comprises a nonwoven synthetic, a backing layer, and a pressure sensitive adhesive layer. The polymeric layer is preferably a polyolefinic material, such as polyethylene, ethylene polyvinyl acetate copolymers, ethylene propylene rubber, polypropylene, polyvinyl chloride, polyisobutylene and conjugated diene butyl. It is said that the polymeric material both coats the nonwoven material and fills the interstices of the nonwoven fibers, so that they will tear substantially evenly only in the direction where the tearing force is exerted.
Despite the work done in the field, there is a need for a nonwoven tape with improved finger-tearability yet with high tensile strength.
The invention provides a nonwoven composite, suitable for use as a backing in adhesive tapes, that has improved finger-tearability due to the incorporation of a woven scrim as one of the layers in a composite.
The nonwoven composite comprises a nonwoven layer and a weft-inserted scrim layer. The nonwoven web is preferably a carded web, and may be embossed with a pattern to enhance finger-tearability. The weft-inserted scrim is a fabric that includes a series of filaments oriented in the machine direction that are interwoven with a series of filaments oriented in the cross direction. The scrim is bonded to the cover web with a bonding solution, which preferably comprises a latex material. The filaments in the scrim provide tear lines in the composite that make it finger-tearable in. both the machine direction and the cross direction.
The invention also provides adhesive tapes, which are made by providing a pressure-sensitive adhesive as an additional layer in the composite.
The invention also provides a method of making the nonwoven composites and tapes of the invention.